Process for the production of titanium dioxide, and titanium dioxide obtained thereby

ABSTRACT

A process for producing a particulate TiO2 includes supplementing metatitanic acid with an alkali compound in a quantity of 1200 ppm to 2400 ppm of alkali, with a phosphorus compound in a quantity of 0.1 wt.-% to 0.3 wt.-% by weight of P, expressed as phosphorus, and with an aluminum compound in a quantity of 1 ppm to 1000 ppm of Al, expressed as Al, to obtain a mixture. The quantity of the alkali compound, of the phosphorus compound, and of the aluminum compound are with respect to the TiO2 content. The mixture is calcined at a constant temperature of 940° C. to 1020° C. until a numerical fraction X50 of TiO2 has a primary crystallite size of at least 200 nm, to obtain a calcined mixture. The calcined mixture is cooled to obtain a cooled calcined mixture. The cooled calcined mixture is grinded to obtain the particulate TiO2.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a divisional of application Ser. No. 16/316,352,filed on Jan. 9, 2019, which is a U.S. National Phase application under35 U.S.C. § 371 of International Application No. PCT/EP2017/065229,filed on Jun. 21, 2017 and which claims benefit to German PatentApplication No. 10 2016 112 682.9, filed on Jul. 11, 2016. TheInternational Application was published in English on Jan. 18, 2018 asWO 2018/010924 A1 under PCT Article 21(2).

FIELD

The present invention relates to a process for the production oftitanium dioxide with a fraction of at most 10% (numerical) ofcrystallites with a size of less than 100 nm, as well as the titaniumdioxide obtained by this process.

BACKGROUND

In the production of titanium dioxide using the sulfate process,titanium dioxide-containing raw materials (slag, ilmenite) are dried andground and then digested with concentrated sulfuric acid. The reactionbetween the raw materials and the concentrated sulfuric acid is carriedout in batches in lined reaction vessels. During the digestion reaction,almost all of the metal oxides present in the raw materials which reactwith sulfuric acid are transformed into the corresponding metalsulfates. After the reaction, a solid mass (digestion cake) remainswhich is dissolved with water and/or dilute sulfuric acid.

This digestion solution, which is known as black liquor, is completelyfreed from the undissolved components (digestion residues, gangue) bysedimentation and/or filtration processes. Further on in the process, asuspension of metatitanic acid is produced from the solids-freedigestion solution by hydrolysis. The metatitanic acid can be suppliedto the downstream process by washing, bleaching and, if appropriate,salt treatment, as well as filtration.

The digestion residues precipitating out during the solid/liquidseparation processes as sediment or filter cake are mashed with waterand/or dilute sulfuric acid and are dumped after neutralization, usuallywith calcium hydroxide suspension and fresh filtration.

Processes for the production of such titanium dioxides are known in theprior art. A process for the production of anatase with large crystalsusing added seed crystals has been described in GB 2 247 009.Alternative processes have been described in EP 0 772 905 and EP 0 782971. However, these processes are all complicated to control and cannotreliably produce an anatase with the desired color stability.

SUMMARY

An aspect of the present invention is to overcome the disadvantages ofthe prior art and in particular also to provide a process for theproduction of titanium dioxide using the sulfate process which can in asimple manner produce a titanium dioxide with a low proportion ofprimary crystallites with a dimension of at most 100 nm.

In an embodiment, the present invention provides a process for aproduction of a particulate TiO₂. The process includes supplementingmetatitanic acid with an alkali compound in a quantity of 1200 ppm to2400 ppm of alkali, with a phosphorus compound in a quantity of 0.1wt.-% to 0.3 wt.-% by weight of P, expressed as phosphorus, and with analuminum compound in a quantity of 1 ppm to 1000 ppm of Al, expressed asAl, to thereby obtain a mixture. Each of the quantity of the alkalicompound, the quantity of the phosphorus compound, and the quantity ofthe aluminum compound are with respect to the TiO₂ content. The mixtureis calcined at a constant temperature of 940° C. to 1020° C. until anumerical fraction X₅₀ of TiO₂ has a primary crystallite size of atleast 200 nm, to thereby obtain a calcined mixture. The calcined mixtureis cooled so as to obtain a cooled calcined mixture. The cooled calcinedmixture is grinded to obtain the particulate TiO₂.

BRIEF DESCRIPTION OF THE DRAWING

The present invention is described in greater detail below on the basisof embodiments and of the drawing in which:

The FIGURE shows an illustration of the measurement procedure and typesof diameter of the present invention.

DETAILED DESCRIPTION

As an example, the process in accordance with the present invention maybe carried out in the following manner: the titanium dioxide-containingraw materials (slag, ilmenite) are dried and ground and then digestedwith concentrated sulfuric acid (for example 90% H₂SO₄). After amaturation period of several hours, for example, the solid mass obtainedfrom digestion of the titanium dioxide raw material is dissolved inwater, for example, with acidified return water. Insoluble componentsare separated in a clarifier. The clarified titanium-containing solutionfrom the clarifier discharge is freed from the remaining solid in filterpresses.

Dissolved trivalent iron is transformed into the divalent form by addingscrap iron, because problematically, Fe²⁺ precipitates out as Fe(OH)₃together with the metatitanic acid and would then be adsorbed on it.Depending on the Fe content, FeSO₄•7 H₂O precipitates out after coolingand is removed from the system.

In the subsequent hydrolysis, metatitanic acid, a precursor of titaniumdioxide, is precipitated out as a solid from the clarified solution byheating and adding water. Advantageously, during the hydrolysis, inaccordance with the present invention no crystallization seeds are addedand the seeds are formed in situ according to Blumenfeld. In the priorart, it is known to hydrolyze titanyl sulfate in order to precipitateout hydrated titanium oxide, either by adding seed crystals(“Mecklenburg” process) or by inducing seed crystals within the solutionby adding water (“Blumenfeld” process).

The metatitanic acid precipitated out during hydrolysis is in the formof a suspension. In one embodiment, the suspension of titanium oxideparticles with formula TiO_((2−x))(OH)_(2x) (0≤x≤1) may be metatitanicacid with formula TiO(OH)₂. Other hydrated forms such as orthotitanicacid are transformed into metatitanic acid by cleavage of H₂O.

This “titanium dioxide suspension” formed by this suspension of titaniumoxide hydrate and/or hydrated titanium oxide particles with generalformula TiO_((2−x))(OH)_(2x) in which (0≤x≤1), or mixtures thereof, can,for example, have the following properties:

-   -   a Ti content, expressed as titanium dioxide, of 50-400 g TiO₂/l,    -   a mean particle size of 20 nm-1000 nm, for example, 20 nm-500        nm, for example, 50 nm-200 nm, for example, 50-150 nm,    -   a specific surface area for the particles of 200-500 m²/g, for        example, 200-400 m²/g, for example, 300-400 m²/g (measured after        drying at 105° C. for at least 120 min, using N₂ porosimetry,        5-point BET),    -   a total pore volume for the particles of >0.3 cm³/g, for        example, >0.5 cm³/g, for example, >0.7 cm³/g (measured after        drying at 105° C. for at least 120 min, using N₂ porosimetry,        5-point BET),    -   the crystalline phases of the particles, after drying at 105° C.        for at least 120 min, are in the anatase phase. After        subtracting a linear background, the ratio of the height of the        most intensive reflection of the anatase structure (reflection        (101)) to the height of the most intensive reflection of the        rutile structure (reflection (110)) is at least 20:1, for        example, at least 40:1. XRD analysis carried out as described in        the section of the text entitled “Methods” in the description        can, for example, exclusively provide reflections of an anatase        structure.

The metatitanic acid formed in this manner may contain free as well asbound sulfuric acid, wherein the crystalline portions of thetitanium-oxygen compounds it contains, as mentioned above, are in theanatase crystal form and have a typical primary crystallite dimension ofapproximately 5-15 nm.

The metatitanic acid is filtered off and washed in washing tanks. Thepasty filter cake is filtered and washed again after an intermediatetreatment.

After cleaning up the metatitanic acid, auxiliary agents are added tothe suspension of this intermediate product prior to calcining; theseauxiliary agents control the growth of the crystals as well as counterrutile formation to some extent.

In accordance with the present invention, alkali components are added asthe auxiliary agents, in particular one or more potassium components, aswell as phosphorus components, in particular phosphates. The potassiumcomponents may also be replaced by a sodium component or a mixture ofthe two.

The phosphorus component may be added in the form of phosphoric acid orin the form of a water-soluble phosphate compound, for example,potassium dihydrogen phosphate. It is used in an amount of at least 0.1%by weight, in particular at least 0.12% by weight and at most 0.3% byweight, in particular at most 0.2% by weight, more particularly, forexample, in the range 0.12% to 0.2% by weight of P, expressed in termsof phosphorus and expressed as the quantity of TiO₂ in the final productin accordance with the present invention. Below the minimum amount of0.1% by weight, rutile formation is greater and above the maximumamount, crystal growth is inhibited as a function of the calciningtemperature.

The potassium components are in particular added in the form of awater-soluble potassium compound, for example, as potassium sulfate oras potassium hydroxide. The potassium may also be used as a counter-ionto the phosphate group, so that the pH of the final product can also beadjusted (pH 7.0 to 8.5). In this regard, in accordance with the presentinvention, depending on the added amount of phosphorus, 1200 to 1400 ppmof potassium with respect to the quantity of TiO₂ is used.

The metatitanic acid washed in the earlier stages which have beendescribed and treated with the alkali and phosphorus components is thendewatered using filtration equipment and supplied to the calciningfurnace. During calcining, water from the supplied TiO₂ filter cake isvaporized, and the sulfuric acid still adhering from digestion isdecomposed and driven off.

Calcining the starting material, which is usually at ambienttemperature, is carried out until a constant temperature is reached, ata temperature of at least 940° C., in particular at least 960° C. andless than 1020° C., in particular less than 1010° C., in particular inthe range 970° C. to 990° C. Calcining is continued at a constanttemperature for a period of time which depends on the calciningtemperature, until the primary crystallites reach the desired size withX₅₀ (mean primary crystallite size with 50% smaller and 50% larger thanthe mean value X₅₀) of at least 160 nm, in particular at least 200 nm,and, for example, less than 300 nm, and the calcined TiO₂ contains aproportion of less than 1.5% by weight of rutile with respect to theweight of the particles. The time period for calcining is usually 40 to300 minutes in the constant temperature range mentioned above.

Because of impurities in the raw materials, in particular niobium, whichcannot be washed out, the anatase product becomes bluer and bluer withincreasing calcining temperature because, in order to compensate for thepentavalent niobium, a reduction of Ti⁴⁺ occurs to form the blue Ti³⁺.To compensate for the color, in accordance with the present invention,an aluminum component is added. The addition may be in the form ofaluminum sulfate or aluminum hydroxide, and the amount added is at least1 ppm, in particular at least 10 ppm and at most 1000 ppm, in particularat most 500 ppm of Al, expressed as Al and with respect to the quantityof TiO₂. Quantities beyond 1000 ppm inhibit the growth of crystals andthen no longer provide the desired properties for the same temperature.A weight ratio of Al₂O₃to Nb₂O₅ of between 0.17 and 0.74 has been shownto be advantageous.

The calcining temperature in cooperation with the added auxiliary agentsprovides a product with the desired properties as regards primarycrystallite size, in particular the specific surface area, proportion ofcrystallites with a proportion of at most 10% (numerical) with adimension of less than 100 nm (nano-fraction) and color.

In accordance with the present invention, a particulate TiO₂ can thus beobtained which may have the following properties:

-   -   a TiO₂ content of at least 99% by weight;    -   an anatase content of more than 98%, in particular more than        98.5% by weight;    -   a primary crystallite size X₅₀ of at least 200 nm, and in        particular at most 300 nm (determined from the numerical        distribution);    -   a numerical fraction of TiO₂ with a primary crystallite size of        at most 100 nm of at most 10% (X₁₀) (determined by counting        these crystallites in TEM or SEM images—Feret method);    -   a specific surface area of at most 8 m²/g, in particular <6 m²/g        (determined by BET measurements);    -   1200 to 2400 ppm of alkali, in particular potassium, with        respect to the quantity of TiO₂;    -   an Al content of at least 1 ppm and at most 1000 ppm of Al,        expressed as Al and with respect to the quantity of TiO₂;    -   a weight ratio of Al₂O₃to Nb₂O₅ in the range 0.17 to 0.74;    -   0.1% by weight and at most 0.3% by weight of P, expressed as        phosphorus and with respect to the quantity of TiO₂ in the final        product; and    -   a proportion of less than 1.5% by weight, in particular less        than 1% by weight of rutile, with respect to the weight of the        particles.

The present invention thus concerns a particulate TiO₂ with thefollowing properties:

-   -   a TiO₂ content of at least 99% by weight;    -   an anatase content of at least 98% by weight;    -   a primary crystallite size X₅₀ of at least 200 nm (determined        from the numerical distribution);    -   a numerical fraction of TiO₂ with a primary crystallite size of        at most 100 nm of at most 10% (X₁₀);    -   a specific surface area of at most 8 m²/g (determined by BET        measurements);    -   1200 to 2400 ppm of alkali, in particular potassium, with        respect to the quantity of TiO₂;    -   an Al content of at least 1 ppm and at most 1000 ppm of Al,        expressed as Al and with respect to the quantity of TiO₂;    -   a weight ratio of Al₂O₃to Nb₂O₅ in the range 0.17 to 0.74; and    -   at least 0.1% by weight and at most 0.3% by weight of P,        expressed as phosphorus and with respect to the quantity of        TiO₂.

A particulate TiO₂ as defined above, with an anatase content of at least98.5% by weight.

A particulate TiO₂ as defined above, with a numerical fraction of TiO₂with a primary crystallite size of at most 100 nm of at most 8%.

A particulate TiO₂ as defined above, with a specific surface area of atmost 6 m²/g (determined by BET measurements).

A particulate TiO₂ as defined above, with a primary crystallite size X₅₀of at most 300 nm.

The present invention also provides a process for the production ofparticulate TiO₂ as defined above, in which metatitanic acid, which is,for example, obtainable using the sulfate process and which is in theform of a suspension, is supplemented with an alkali compound in aquantity of 1200 to 2400 ppm of alkali, a phosphorus compound in aquantity of at least 0.1% by weight and at most 0.3% by weight of P,expressed as phosphorus, and an aluminum compound in a quantity of atleast 1 ppm and at most 1000 ppm of Al, expressed as Al, wherein all ofthe quantities are respectively with respect to the quantity of TiO₂,is, for example, dewatered and dried and then undergoes calcining in amanner such that the particulate TiO₂ is held at a constant temperatureof between at least 940° C. and at most 1020° C. for a period of timeuntil the numerical fraction X₅₀ of TiO₂ has a primary crystallite sizeof at least 200 nm, and the particulate TiO₂ obtained after coolingundergoes a grinding treatment, in particular a dry grinding.

Because of its smaller quantities of particle sizes in the nanometerrange, the TiO₂ material in accordance with the present invention issuitable for those applications in which such a proportion of suchparticle sizes might be considered to be unsafe, for example, in thefield of foodstuffs, pharmaceuticals, cosmetics and care products forthe human body, as well as in polymers which are used as packaging forfoodstuffs or as fibers. In the latter applications, the TiO₂ materialin accordance with the present invention advantageously undergoes asubsequent treatment with an organic compound. The present inventiontherefore also concerns:

-   -   particulate TiO₂ as described above, wherein at least a portion        of the surface of the particles has been coated with an organic        compound or mixtures thereof;    -   particulate TiO₂ as described above, wherein the organic        compound is selected from polyglycols including polyethylene        glycols, polypropylene glycols or copolymers thereof, carboxylic        acids and their alkali salts, polyvalent alcohols, including        trimethylolpropane, trimethylolethane, pentaerythritol and        neopentyl glycol, silanes, siloxanes and siloxane derivatives,        silicone oils, alkali salts of polyphosphates, amino alcohols,        salts of poly(meth)acrylic acid or poly(meth)acrylate copolymers        (for example, sodium, potassium or ammonium polyacrylates) or        mixtures thereof; and    -   particulate TiO₂ as described above, wherein the organic        substance is used in a quantity of 0.01% to 8% by weight, for        example, 0.05% to 4% by weight, for example, 0.1% to 1.5% by        weight, with respect to the total weight of the particulate        TiO₂.

EXPERIMENTAL SECTION Description of the Measurement Methods UsedDetermination of Mean Particle Size

In order to determine the mean particle size of titanium oxide withgeneral formula TiO_((2−x))(OH)_(2x) in which 0≤x≤1, the aqueous“titanium oxide suspension” was initially diluted in a solution of 1 gof Calgon/l of deionized water in order to produce a concentration ofapproximately 0.4 g of TiO₂ in 60 ml of solution. The “titanium oxide”suspension diluted in this manner was initially dispersed for 5 min inan ultrasound bath (for example, a Sonorex Super RK106, from Bandelin)with stirring, and then dispersed for 5 min with an ultrasound finger(Sonifier® W-450 from Branson with a gold booster for amplitudereinforcement and ¾ inch horn). The particle size distribution wasdetermined by a photon correlation spectrometer using Zetasizer AdvancedSoftware, for example the Zetasizer 1000HSa, from Malvern. A measurementwas carried out with multimode acquisition at a temperature for themeasurement of 25° C. The mean particle size d₅₀ given was the d₅₀ valuefor volume distribution, which corresponds to the mass distribution withdensity taken into account.

Determination of Phase and Crystallite Size in Accordance with Scherrer

In order to determine the crystal phase (phase identification), an X raydiffractogram was recorded. On it, the intensities according to theBragg relationship of the X rays deflected by the lattice planes of acrystal were measured against the angle of deflection 2 theta. A phasehas a typical X ray diffraction diagram.

Measurement and Analysis

The material to be investigated was painted onto the preparation supportwith the aid of an object carrier. The powder diffractometry data wasanalyzed with the aid of the JCPDS powder diffractometry database. Thephase was identified when the measured diffraction diagram matched therecorded pattern of spots.

Typical measurement conditions were as follows: 2 theta=10°-70°,measured in steps of 2 theta=0.02°, measurement period per step: 1.2 s.

The crystallite size was determined using the Scherrer method from thehalf-height widths of the anatase reflection at a 2 theta of 25.3° usingthe following formula:

D crystallite=K*l/(S*cos(theta)

wherein:

D crystallite: crystallite size [nm]

K: shape constant=0.9

theta: angle of measured reflection 2 theta/2

S: half-height width of measured reflection

l: wavelength of X ray beam used.

Determination of Specific Surface Area (Multipoint Method) and Analysisof Pore Structure using the Nitrogen Gas Adsorption Method (N₂Porosimetry)

The specific surface area and the pore structure (pore volume and porediameter) were determined by N₂ porosimetry using the Autosorb® 6 or 6Binstrument from Quantachrome GmbH. The BET (Brunnauer, Emmet and Teller)specific surface area was determined in accordance with DIN ISO 9277;the pore distribution was measured in accordance with DIN 66134.

Sample Preparation (N₂ Porosimetry)

The sample weighed into the measurement cell was initially dried in theheating station for 16 h under vacuum. Next, it was heated under vacuumto 180° C. over approximately 30 min. The temperature was thenmaintained for one hour, still under vacuum. The sample was consideredto have been sufficiently degassed when in the degasser a pressure of20-30 millitorr was set and, after uncoupling the vacuum pump, theneedle on the vacuum gauge remained stable for approximately 2 min.

Measurement/Analysis (N₂ Porosimetry)

The entire N₂ isotherm was measured using 20 adsorption points and 25desorption points. The measurements were analyzed as follows:

Specific Surface Area (Multi-Point BET)

5 measurement points in the analysis range of 0.1 to 0.3 p/p0

Total Pore Volume Analysis

The pore volume was determined in accordance with the Gurvich rule(determination from the last adsorption point).

The total pore volume was determined in accordance with DIN 66134,applying the Gurvich rule. In accordance with what is known as theGurvich rule, the total pore volume of a sample is determined from thefinal pressure point in the adsorption measurement:

p. pressure of adsorptive

p0. saturated vapor pressure of adsorptive

Vp. specific pore volume in accordance with Gurvich rule (total porevolume at p/Po=0.99) reached by quasi-final adsorption pressure pointobtained from the measurement.

Determination of Mean Pore Diameter (Hydraulic Pore Diameter):

The relationship 4Vp/A_(BET) was used for the calculation, correspondsto the “Average Pore Diameter”. A_(BET) specific surface area inaccordance with ISO 9277.

Crystallite Size Determination of Calcined TiO₂ Samples

The method determines dimensional data of pigment crystallites, such asthe number and volume distribution, the nano-fraction, shape informationand typical parameters such as X₁₀, X₅₀ and X₉₀. With the aid ofelectron microscope images, the edges of the crystals were outlinedusing a touch-sensitive screen. The object data obtained in this mannerwere brought together in an overall distribution.

The pigment was dispersed with a solvent and the suspension was dried ona support. A SEM and/or TEM image was produced at four differentlocations of the support. If a nanoclassification was to be carried outin accordance with EU regulations, then the magnification must be atleast V=50000.

The SEM or TEM images were analyzed using Image Pro Plus software withthe aid of a macro. The outer edges of the individual crystallites werehere outlined with the stylus, as can be seen in the Figure, which showsan illustration of the measurement procedure and types of diameter.

In total, at least 500 particles must be assessed on all the images. Thedimensional data obtained in this manner was analyzed using an Excelspreadsheet.

The analysis contains:

-   -   volume and numerical distribution of the mean (primary)        crystallite diameter (ECD)    -   numerical distribution of the smallest (primary) crystallite        diameter (Feret min)    -   nano-fraction in accordance with EC regulations    -   X₁₀, X₅₀, X₉₀ distribution data

In order to determine the nano-fraction, the smallest diameter flank(Feret_(min)) and the mean diameter from the crystal size data (ECD:Equivalent) were determined. The calibration was carried out from thescale bars of each individual image.

Determination of Titanium, Expressed as TiO₂

Determination of TiO₂ content on pressed powder pellets using X rayfluorescence analysis (XRFA)

Determination of Al

The Al content of the pressed powder pellets was determined using X rayfluorescence analysis (XRFA).

Determination of P

The P content of the pressed powder pellets was determined using X rayfluorescence analysis (XRFA).

Determination of Nb

The Nb content of the pressed powder pellets was determined using X rayfluorescence analysis (XRFA).

Determination of K

The K content of the pressed powder pellets was determined using X rayfluorescence analysis (XRFA).

Determination of Colorimetric Measurement b* (in accordance with CIELAB,DIN 6174 or ISO 7724/2)

Determination of colorimetric measurements L*, a*, b* using the CIELABsystem from the measurement of the standard color values X, Y, Z ofpressed powder pellets using the Color Eye 7000A measurement system(pellets produced in accordance with DIN 5033 T9).

Measurement protocol: illuminant C, 2° standard observer, measurementgeometry: 45/0

The invention will be explained in more detail by means of the followingComparative Examples and Examples.

Comparative Example A

A titanyl sulfate solution containing 230 g/l of TiO₂ was obtained usingthe known sulfate process for the production of titanium dioxide bydigesting titanium slag in concentrated sulfuric acid, then dissolvingthe digestion cake obtained in water and separating the undigestedresidues. In a subsequent Blumenfeld hydrolysis, metatitanic acid, aprecursor of titanium dioxide, was precipitated out of the titanylsulfate solution as a solid by heating to 98° C. and adding hot water.The metatitanic acid precipitated out during the hydrolysis was washedat a temperature of 80° C. on suction filters with 81 of demineralizedwater per kg of TiO₂, and then treated for 1 hour at 80° C. with Ti(III)solution in order to remove adsorbed heavy metals and then washed againon a suction filter with 8 l of demineralized water per kg of TiO₂.Next, the filter cake was elutriated with water to 300 g/l of TiO₂(washed metatitanic acid).

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂) and85% phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂)were added with stirring to 6 kg of this washed metatitanic acid in amixing tank with a propeller stirrer, stirring was continued for afurther 1 hour, drying was carried out in a drying cabinet at 105° C.and then calcining was carried out in batches for 90 min at 930° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Comparative Example B

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂ with water.

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO2) andaluminum hydroxide powder (110 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 930° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Comparative Example C

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂ in water.

25% potassium hydroxide (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) andaluminum sulfate powder (110 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 930° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Comparative Example D

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂ with water.

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 980° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Comparative Example E

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂ with water.

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) andaluminum hydroxide powder (110 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 1040° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Comparative Example F

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂, with water.

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) andaluminum hydroxide powder (1000 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 980° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Comparative Example G

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂ with water.

Potassium sulfate powder (1100 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.09% by weight of phosphorus expressed as TiO₂) andaluminum hydroxide powder (110 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 930° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Example 1

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂, with water.

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) andaluminum hydroxide powder (110 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 980° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Example 2

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂, with water.

25% potassium hydroxide (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) andaluminum hydroxide powder (110 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 980° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

Example 3

A washed metatitanic acid was produced as described in ComparativeExample A and adjusted to 300 g/l of TiO₂, with water.

Potassium sulfate powder (1650 ppm of potassium expressed as TiO₂), 85%phosphoric acid (0.14% by weight of phosphorus expressed as TiO₂) andaluminum hydroxide powder (60 ppm of aluminum expressed as TiO₂) wereadded with stirring to 6 kg of this washed metatitanic acid in a mixingtank with a propeller stirrer, stirring was continued for a further 1hour, drying was carried out in a drying cabinet at 105° C. and thencalcining was carried out in batches for 90 min at 980° C. in alaboratory muffle furnace. The calcined material was ground in a spiraljet mill.

TABLE 1 Summary of Experimental Conditions K P Al Calcining K added Padded Al added temperature Example component [ppm] component [%]component [ppm] [° C.] A K₂SO₄ 1650 H₃PO₄ 0.14 None 0 930 B K₂SO₄ 1650H₃PO₄ 0.14 Al(OH)₃ 110 930 C KOH 1650 H₃PO₄ 0.14 Al₂(SO₄)₃ 110 930 DK₂SO₄ 1650 H₃PO₄ 0.14 None 0 980 E K₂SO₄ 1650 H₃PO₄ 0.14 Al(OH)₃ 1101040 F K₂SO₄ 1650 H₃PO₄ 0.14 Al(OH)₃ 1000 980 G K₂SO₄ 1100 H₃PO₄ 0.09Al(OH)₃ 110 980 1 K₂SO₄ 1650 H₃PO₄ 0.14 Al(OH)₃ 110 980 2 KOH 1650 H₃PO₄0.14 Al₂(SO₄)₃ 110 980 3 K₂SO₄ 1650 H₃PO₄ 0.14 Al(OH)₃ 60 980

TABLE 2 Results Crystallite Nano- Anatase TiO₂ Size Fraction BET ExampleAl₂O₃/Nb₂O₅ [%] [%] X₅₀ [nm] [% <100 nm] [m²/g] CIE b* A — 98.9 99.1 10049 10.7 0.2 B 0.66 99.1 99.0 98 52 10.8 0.3 C 0.66 98.6 99.0 95 58 11.10.3 D — 98.6 99.2 218 5 5.3 −1.7 E 0.66 97.5 99.1 293 2 3.0 1.2 F 6.0098.9 98.9 180 17 8.8 1.6 G 0.66 98.0 99.3 237 3 4.8 0.9 1 0.66 98.8 99.0213 7 5.5 0.7 2 0.66 98.9 99.0 208 4 5.2 0.7 3 0.36 98.7 99.1 215 5 5.40.5

Visual Perceived Color by Observer of TiO₂ Powder

CIE b*>0.5 yellowish white

CIE b* 0 to 0.5 neutral white

CIE b*<0 bluish white

The product in accordance with the present invention is distinguished bya crystallite size with a small numerical fraction of crystallites of atmost 100 nm of at most 10%, with a warm shade, which is of advantage, inparticular with cosmetic products.

The present invention is not limited to embodiments described herein;reference should be had to the appended claims.

What is claimed is:
 1. A process for a production of a particulate TiO₂,the process comprising: supplementing metatitanic acid with, an alkalicompound in a quantity of 1200 ppm to 2400 ppm of alkali, a phosphoruscompound in a quantity of 0.1 wt.-% to 0.3 wt.-% by weight of P,expressed as phosphorus, and an aluminum compound in a quantity of 1 ppmto 1000 ppm of Al, expressed as Al, to thereby obtain a mixture,wherein, each of the quantity of the alkali compound, the quantity ofthe phosphorus compound and the quantity of the aluminum compound arewith respect to the TiO₂ content; calcining the mixture at a constanttemperature of 940° C. to 1020° C. until a numerical fraction X₅₀ ofTiO₂ has a primary crystallite size of at least 200 nm, to therebyobtain a calcined mixture; cooling the calcined mixture so as to obtaina cooled calcined mixture; and grinding the cooled calcined mixture toobtain the particulate TiO₂.
 2. The process as recited in claim 1,wherein the metatitanic acid is obtained using the sulfate process andis provided as a suspension.
 3. The process as recited in claim 1,further comprising: dewatering the mixture; and drying the mixture. 4.The process as recited in claim 1, wherein the grinding is a drygrinding.
 5. The process as recited in claim 1, wherein the particulateTiO₂ comprises: a TiO₂ content of at least 99 wt.-%; an anatase contentof at least 98 wt.-%; a primary crystallite size X₅₀ of at least 200 nm;a numerical fraction of TiO₂ with a primary crystallite size of at most100 nm of at most 10%; a specific surface area of at most 8 m²/g asdetermined by BET measurements; 1200 ppm to 2400 ppm of alkali withrespect to the TiO₂ content; an Al content of 1 ppm to 1000 ppm,expressed as Al and with respect to the TiO₂ content; a weight ratio ofAl₂O₃to Nb₂O₅ of from 0.17 to 0.74; and 0.1 wt.-% to 0.3 wt.-% of P,expressed as phosphorus and with respect to the TiO₂ content.
 6. Theprocess as recited in claim 5, wherein the alkali is potassium.
 7. Theprocess as recited in claim 5, wherein the anatase content is at least98.5 wt.-%.
 8. The process as recited in claim 5, wherein the numericalfraction of TiO₂ with the primary crystallite size of at most 100 nm isat most 8%.
 9. The process as recited in claim 5, wherein the specificsurface area is at most 6 m²/g.
 10. The process as recited in claim 5,wherein the primary crystallite size X₅₀ is at most 300 nm.
 11. Theprocess as recited in claim 5, wherein, the particulate TiO₂ comprisesparticles, and the process further comprises: coating at least a portionof a surface of the particles with an organic compound or with mixturesof organic compounds.
 12. The process as recited in claim 11, whereinthe organic compound is selected from polyglycols, carboxylic acids andtheir alkali salts, polyvalent alcohols, silanes, siloxanes and siloxanederivatives, silicone oils, alkali salts of polyphosphates, aminoalcohols, salts of poly(meth)acrylic acid or poly(meth)acrylatecopolymers, or mixtures thereof.
 13. The process as recited in claim 12,wherein, the polyglycols are selected from polyethylene glycols,polypropylene glycols or copolymers thereof, the polyvalent alcohols areselected from trimethylolpropane, trimethylolethane, pentaerythritol andneopentyl glycol, and the salts of poly(meth)acrylic acid orpoly(meth)acrylate copolymers are selected from sodium, potassium orammonium.
 14. The process as recited in claim 12, wherein the organiccompound is used in a quantity of 0.01 wt.-% to 8 wt.-% with respect toa total weight of the particulate TiO₂.